How can I disable text selection using shift without disabling all text selection?

How can I disable text selection using shift without disabling all text
selection?

So I know this sounds like a duplicate, but it isn't (or if it is, the
accepted answer on all the ones I can find doesn't work the way I need it
to). The issue is this:
I'm writing in HTML5 using jQuery, I need to make a grid allow
multi-select with control and shift. I have that logic working, but
whenever you shift-click it selects the text in the grid. I want to
prevent this selection, but here's the critical difference between this
and the other questions I found: I want selection of text to work at all
other times.
To restate: I want to disable text selection using shift WITHOUT disabling
all text selection for the elements specified. Does anyone know how I can
do that?